1. Field of the Invention
The present invention is directed to an electroencephalographic (EEG) cap for making EEG measurements and, more particularly, is directed to an EEG cap having self-preparing electrodes, for use in an evoked potential autorefractometry system which prescribes eyeglass lenses as described in the copending application mentioned above.
2. Description of the Related Art
FIG. 1A illustrates a prior art flexible EEG cap 10 having non-self-preparing electrodes 11 attached to flexible fabric 12 of the cap 10. The electrodes 11 do not directly contact the skin of the patient, but do so through an electrolyte cream. When this cap 10 is used, a blunt hypodermic needle must be inserted into a hole 13 in each electrode 11 and used to abrade the underlying skin to remove a keratinous layer or dead layer of skin so that the electrolyte cream, which is ejected from the syringe during removal will provide electrical contact between an epidermis layer of skin and the electrode 11.
If the hair beneath the point of contact of the electrodes 11 in the prior art cap 10 is very thick, it is sometimes necessary to cut the hair in order to allow the electrodes 11 to get close enough to the scalp so that the electrode cream does not create excessive resistance. FIG. 1B illustrates the details of the prior art cap electrode 11 in more detail. A plastic electrode body 14 is held to the fabric 12 by a press fit gromet 15, includes a metal conductor or slug 16 and forms a cavity 17 between the skin and the conductor 16. When electrolyte cream is injected through hole 13, it completes the electrical connection to the skin.
This prior art cap 10 is not suitable for commercial use in an evoked potential autorefractometry system because it is intimidating to potential patients and great discomfort is caused during the preparations for EEG measurement due to the necessary abrasion of the skin. The process undesirably requires the application of substantial amounts of electrode cream which patients remove from the hair by washing for cosmetic purposes after the cap 10 is removed. The electrical conductors 18 traveling from the electrodes 11 to the testing apparatus are not shielded and can pick up substantial amounts of environmental noise which makes the measurement of EEG signals much more difficult. In addition, different size caps 10 must be provided for patients of different sizes. The prior art cap 10 and electrodes 11 are described in more detail in U.S. Pat. Nos. 4,085,739 and 4,323,076.